A Search for Very High-Energy Gamma Rays From the Missing Link Binary Pulsar J1023+0038 With VERITAS Print

 

 

Broadband spectrum of PSR J1023+0038 after the reappearance of the accretion disk. For details, see Figure 3 below.

Reference: E. Aliu et al. (The VERITAS Collaboration), Astrophysical Journal 831: 193 (2016)

Full text version

ArXiv: ArXiV:1609.01692

Contacts: Greg Richards

PSR J1023+0038 is a low-mass X-ray binary system located at a distance of 1.37 kpc that consists of a a millisecond pulsar (MSP) with a rotation period of 1.69 ms in orbit around an ordinary G star.  In June of 2013, this system was the first ever to be caught in the act of "recycling:" the radio pulsar was seen to disappear, indicating that the pulsar in the system intermittently accretes material from the companion star.  It is thought that MSPs are spun up to their small, milliseconds-long rotation periods through this process called recycling.  Since PSR J1023+0038 was the first such system observed to toggle the accretion mechanism off and on, it has been referred to as "the missing-link binary pulsar."

PSR J1023+0038 has several characteristics that are similar to the very high-energy (VHE) gamma-ray-emitting binary system PSR B1259-63/LS 2883, which were responsible for its initial selection as a target for VERITAS observations.  Further, it has been the subject of multi-wavelength campaigns after the disappearance of the pulsed emission in 2013, after which an accretion disk was detected around the neutron star.  VERITAS collected VHE gamma-ray data on PSR J1023+0038 both before and after this change of state, though searches for steady and pulsed emission in both data sets yield no significant gamma-ray signal in the VHE band.  Given that no gamma-ray detection was made, upper limits are calculated for both a steady and pulsed gamma-ray flux. These upper limits can be used to constrain the magnetic fi eld strength in the shock region of the PSR J1023+0038 system. Assuming that very high-energy gamma rays are produced via an inverse-Compton scattering mechanism in the shock region, the VERITAS upper limits constrain the shock magnetic field strength to be greater than 2 G before the disappearance of the radio pulsar and greater than 10 G afterwards.

 

FITS files:

 

Figures from paper (click to get full size image):

 


Figure 1:  Light curve of events phase-folded with the Jodrell Bank radio ephemeris for the radio MSP state.  The light curve shows two pulsar periods and contains 30 bins per period.  The dashed and dotted red lines represent the average number of counts and error on the average, respectively.
Figure 2: Broadband spectrum of PSR J1023+0038 during the millisecond pulsar phase. Thick blue bars show the detection of the X-ray emission by XMM-Newton in 2008 (Archibald et al. 2010) and the Fermi-LAT GeV  detection (Tam et al. 2010). The black solid line represents synchrotron emission in a 40 G magnetic field, and the black dashed line represents the component due to inverse-Compton scattering of optical photons. The solid and dashed green lines represent those same components in the case of a 2 G magnetic field. The red dashed line represents a typical power-law model with an exponential cut-off spectrum of a GeV millisecond pulsar. The arrow represents the VERITAS flux upper limit reported in this work.

Figure 3: Broadband spectrum of PSR J1023+0038 after the reappearance of the accretion disk. The thick blue bar shows the X-ray emission detected by Swift in 2013 November (Takata et al. 2014). Black triangles represent the Fermi-LAT HE gamma-ray detection in 2013 (Takata et al. 2014).  The arrow shows the VERITAS upper limit for the accretion/LMXB state, as reported in this work. Solid and dashed lines correspond to the synchrotron and inverse-Compton emission coming from the shock for the case of a 10 G (green lines) and 80 G (black lines) magnetic field. The spectral signature of inverse-Compton scattering of photons emitted by the accretion disk on the unshocked electrons is shown with a red dash-dotted line.


Last Updated on Friday, 13 January 2017 11:17